1. Field of the Invention
This invention relates generally to the field of ion sources and the ion beams extracted from them. More particularly, the invention relates to ion implantation. Yet more particularly the invention relates to ion implantation for flat panel displays.
2. Description of Related Art
Ion implantation into large areas has been attempted in the past by use of an ion shower system, reported by M. Tanjyo, et al. in the article, Development of a Mass Separation Structure for Large Area Ion Source, Ion Implantation Technology-92, Proc. 9th Int'l Conference on Ion Implantation Technology, Gainesville, Fla., pg. 445 to 448, Ed. D. F. Downey et al., Elsevier Science Publishers B. V. 1993 and in U.S. Pat. No. 5,189,303: "Ion Source having a Mass Separation Device", M. Tanjyo and H. Nakazato. The ion shower system comprises an approximately parallel ion beam extracted from a multi-hole extraction electrode that gives rise to many parallel beamlets. The array of beamlets yields a beam diameter of 220 mm. It is very difficult with this beamlet system to separate unwanted ion species, that may be generated in the ion source along with the wanted species, out from the final beam. Tanjyo suggested solving this problem by placing a mass spectrometer at each beamlet aperture. This approach is mechanically cumbersome, expensive, and problematic in several other ways.
Another approach to implanting a large area substrate is to produce a small ion beam and scan it back and forth across the substrate. N. Nagai et al. describe a beam scanning system in Sweep Uniformity Control System in the NISSIN NH-20SP, Ion Implantation Technology-92, Proc. 9th Int'l Conference on Ion Implantation Technology, Gainesville, Fla., pg. 457 to 460, Ed. D. F. Downey et al., Elsevier Science Publishers B. V. 1993. However a beam scanning system is slow and subject to alignment difficulties which can affect the uniformity of the implantation process. Additionally, as the beam scans across large area substrate, the angle of incidence of ions approaching the substrate changes. This results in problematic changes in ion penetration, density, and uniformity.
A variation in scanning the beam across the substrate is reported by Derek Aitken in his abstract, Ion Implantation Equipment for Flat Panel Displays. He suggests extracting a ribbon beam, by which he presumably means a rectangularly shaped beam, and mechanically scanning the substrate through the beam along a single axis, presumably in the direction of the short axis of the rectangle. This type of system suffers from the disadvantage of being expensive and mechanically cumbersome. It additionally requires more manipulation of the fragile and carefully aligned target than is desirable. In the case of flat panel displays, where the target is a thin glass sheet, the target could be easily damaged by such a process.